Try replugging the cables and connections first before concluding that it has failed – half of all ‘failures’ are problems with connections. Or shut down the machine, turn off the hard drive. Now turn on the hard drive first, let it come up to speed, and then boot the computer.
There are 3 main possibilities if your external drive still won’t mount:
#1 is that the logical structure of the drive is damaged. The good news is that this can often be fixed with software, and although some files may be lost, there is a good chance of recovering most of them.
#2 is that the enclosure (powersupply or the bridge board or its cable connections) is bad. In that case you are in luck because if you can remove the drive mechanism from the case, and put it in a different external USB case, it should work. (this may however void the manufacturer’s warranty if it was a finished-goods external drive)
#3 is that the drive mechanism itself has failed. In that case you may be up a creek. If the motor isn’t spinning the drive, or if the drive’s controller board has burned out, then nothing short of repair by an expert is going to help. Data recovery firms will fix it, but for a fee of $400 – $ several thousand.
If your problem is logical (#1)
— that is the drive spins properly and shows up on the USB bus but there are no accessible partitions or data —
then you may be able to recover data from it, or repair the logical damage. Programs like SpinRite from GRC labs and Ontrack utilities might repair the damage, programs like DataRescue PC, Pandora and others might recover data even if the directories and file structure are damaged.
Windows
SpinRite http://www.grc.com/spinrite.htm
Diskinternals Partition Recovery http://www.diskinternals.com/products.shtml
OnTrack software http://www.ontrackdatarecovery.com/file-recovery-software/
Pandora Recovery http://www.pandorarecovery.com/
DataRescue PC http://www.prosofteng.com/products/data_rescue_pc.php
Easeus has a variety of recovery tools, from free to professional: Download.com link
Recuva (free) http://www.piriform.com/recuva
Restoration (free) http://download.cnet.com/Restoration/3000-2094_4-10322950.html?tag=mncol
Recovery Review – list of recovery software http://recovery-review.com/
Mac:
Repair
Apple’s DiskUtility http://support.apple.com/kb/TS1417
Alsoft DiskWarrior http://www.alsoft.com/DiskWarrior/
TechTool Pro http://www.micromat.com/
Recovery
MiniTool lMac http://mac.powerdatarecovery.com/
DataRescue http://www.prosofteng.com/
FileSalvage (Mac) http://subrosasoft.com/OSXSoftware/index.php?main_page=product_info&products_id=1
Article on recovery http://en.wikipedia.org/wiki/Data_recovery
There are some websites that have tools you can try, and then if it looks like it can recover some data, you have to pay to do the recovery
VirtualLab http://www.binarybiz.com/
If all else fails, you can send your drive to a data recovery service, it will cost hundreds or thousands of dollars depending on what the problem is.
If you are going to send it out for recovery, the less fooling around with software you do with the drive on your own, the better.
Seagate Data Recovery http://services.seagate.com/consumer_solutions.aspx
DriveSavers http://www.drivesavers.com/
ActionFront http://www.actionfront.com/
TotalRecall http://www.totalrecall.com/